(1) Field of the Invention
The present invention relates to a plastic container used for packaging of foods, etc., which is easily recyclable after use. More particularly, the present invention relates to a recyclable plastic container which, after the use by consumers, can be recovered in a state not stained with any contents even if no washing of container is made.
(2) Description of the Prior Art
In recent years., use of food-packaging containers made of a plastic has rapidly spread for various reasons such as (1) the containers can be produced on a large scale, (2) they can be formed in any desired shape, (3) they enable automatic filling and packaging, (4) they are lightweight and easy to handle, (5) they are resistant to breakage, (6) they are easy to color or apply printing thereon, (7) they can be produced at a low cost, and (8) they can be produced from a material(s) appropriately selected from various plastics so as to meet the applications. For example, in packaging of foods such as lunch box, side dishes to be taken with rice, and the like, polystyrene containers are in wide use because of excellent productivity. It is often conducted to heat lunch boxes, etc. in a microwave oven and, in such a case, heat resistance is required for the containers; therefore, food-packaging containers made of polypropylene or the like are used for such purposes.
Meanwhile, with the spread of. plastic containers, the public hazard caused by discarded plastic containers and the effective utilization of resources have come to be taken up as an important problem or task. Hence, there has arisen a movement that producers of plastic containers recover plastic containers after use. The recovery ratio, however, is relatively low yet. While the plastic containers to be recycled need be washed, consumers are very reluctant to wash used containers stained with foods and, moreover, washing of stained plastic containers after recovery requires a very large expense. For these reasons, the recovery ratio of used plastic containers has been low and the recycling of plastic containers has made no substantial progress.
Under such a situation, there is proposed in, for example, Japanese Utility Model Laid-Open No. 4-38942 (1992of a container by peeling of a film present at the inside of the container after the use of the container. However, there has been no good proposal as to the recovery and recycling of a container formed by laminating different kinds of films. Meanwhile, in Japanese Utility Model No. 7-56190 (1985) is disclosed a technique of, in a container comprising (1) a base layer (made of a foamed synthetic resin) and (2) a surface layer (e.g. a synthetic resin film), peeling the surface layer from the base layer to recover the base layer. In this technique, however, the peeling strength between the base layer and the surface layer is 50 to 500 g/15 mm (width), and this strength is too large for manual peeling.
The present inventions aims at providing a plastic container which, after the use, can be easily recovered in a state not stained with any contents even if no washing of container is made.
In order to provide such a plastic container, the present inventors made a study on a technique wherein (1) the inner surface film of a plastic container can be manually peeled, after the use of container, more easily than in containers of past proposals, (2) the contents left over in the container can be completely removed by the above peeling, and (3) the container can be recovered in a clean state not stained with any contents. (This technique enables the reuse of recovered container and the use of peeled film as a fuel.) As a result, the present inventors found out such a resin composition used in container and such a container structure as to give an appropriate adhesion strength and resultantly be able to provide a plastic container wherein the surface film is not peeled from the main portion of container during production or use of container but, after the use of container, can be peeled more easily than in conventional plastic containers. The present invention has been completed based on the above finding. The present invention is as follows.
1. An easily recyclable container obtained by subjecting a sheet L which is a laminate of a plurality of layers, to vacuum forming and/or pressure forming, in which container
the sheet L has such two adjacent layers as to give the minimum peeling strength and can be manually separated into two portions at the interface of the two adjacent layers,
when the portion of the sheet L present from the interface of said two adjacent layers to the inner surface of the container is named as film portion F and the portion of the sheet L present from said interface to the outer surface of the container is named as sheet portion S, the film portion F is a single-layered film or a multi-layered film comprising two or more layers and the sheet portion S is a single-layered sheet or a multi-layered sheet comprising two or more layers,
when one of said adjacent layers giving the minimum peeling strength, belonging to the film portion F is named as layer FS and the other layer belonging to the sheet portion S is named as layer SF, either of the layer FS and the layer SF comprises a resin composition containing the following component (A) in an amount of 50 to 99% by weight and the following component (B) in an amount of 1 to 50% by weight (this layer is named as layer P) and the other layer comprises, as a resin, the component (A) other than used in the layer P and comprises no component (B) (this layer is named as layer Q),
thereby, the peeling strength required for peeling of the film portion F from the sheet portion S is set at 2 to 45 g/15 mm (width).
(A) One kind of resin selected from polystyrene, polypropylene and polyethylene.
(B) At least one kind of polymer other than the component (A), having a solubility parameter (SP) of 8.40 to 8.70.
2. A container according to the above 1, wherein the collar has a part making easier the peeling of the film portion F.
3. A container according to the above 2, wherein the collar part making easier the peeling of the film portion F is a tongue or a notched part formed in the collar so that the notched part can be bent and pulled manually.
4. A container according to any of the above 1 to 3, wherein the proportions of the component (A) and the component (B) in the resin composition containing these two components are 75 to 99% by weight [the component (A)] and 1 to 25% by weight (the component (B)).
5. A container according to any of the above 1 to 4, wherein the resin constituting the layer Q is a polyethylene and the component (A) in the layer P is a polystyrene.
6. A container according to any of the above 1 to 4, wherein the resin constituting the layer Q is a polypropylene and the component (A) in the layer P is a polyethylene or a polystyrene.
7. A container according to any of the above 1 to 4, wherein the resin constituting the layer Q is a polystyrene and the component (A) in the layer P is a polypropylene or a polyethylene.
8. A container according to any of the above 1 to 4, wherein the resin constituting the layer Q is a decomposable polyethylene and the component (A) in the layer P is a polystyrene.
9. A container according to any of the above 1 to 8, wherein the component (B) is at least one kind of copolymer selected from copolymers of ethylene and at least one vinyl monomer selected from unsaturated carboxylic acids, unsaturated carboxylic acid esters and vinyl acetate, and styrene copolymers.
10. A container according to the above 9, wherein the component (B) is at least one kind of copolymer selected from ethylene-methyl methacrylate copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer and styrene-butadiene copolymer.
11. A container according to any of the above 1 to 10, wherein, when the sheet portion S is a multi-layered sheet, at least one layer of the sheet portion S other than the layer SF contacting with the film portion F is made of a foamed synthetic resin.
12. A container according to any of the above 1 to 11, wherein, when the sheet portion S is a multi-layered sheet, at least one layer of the sheet portion S other than the layer SF contacting with the film portion F contains at least one kind of recycled resin selected from polystyrene, polyethylene, polypropylene, and polymers having a solubility parameter (SP) of 8.40 to 8.70.
13. A container according to any of the above 1 to 12, wherein the peeling strength needed for peeling of the film portion F from the sheet portion S is 2 to 25 g/15 mm (width).
14. A container according to any of the above 1 to 13, wherein the sheet portion S and the film portion F have been laminated by melt-extruding a sheet portion S onto a running film portion F.
15. A container according to any of the above 1 to 14; which is used for foods.